The present invention generally relates to a light detector apparatus and, in particular, relates to such a detector apparatus adaptable for use in ion chromatography.
In general, liquid chromatography is an analytical technique which frequently employs light absorption detectors to determine the presence or absence of a material in the eluent of a chromatographic separating column. Such detectors ordinarily are quite expensive due to the necessary optical elements required. For example, such a detector can often include such elements as a scanning monochromator, numerous lenses and mirrors as well as a rather expensive light source. In addition, such an apparatus is usually required to be clean, stable and aligned.
One application of liquid chromatography, however, does not ordinarily employ a light absorption detector. This application is generally referred to as ion chromatography and, because of the ionic nature of the analytes, usually employs a conductivity detector. Due to its multielement capability, the use of ion chromatography is attractive for the direct determination of metals in a variety of sample matrices.
However, one limitation of the application of ion chromatography to metals is the lack of specificity of the conductivity detector. Present conductivity detectors often cannot distinguish a small conductivity change due to the element of interest because it is superpositioned on a high conductivity mobile phase. Consequently, a weakly conducting solvent material has been required in order to be able to distinguish the presence of a metal therein. However, the use of such weak mobile solvents restricts the flexibility of the chromatographic system since high conductivity mobile phases are excluded.